Generally, internal combustion engines take two forms, four-stroke systems or two-stroke systems. In a four stroke system, a combustion process occurs through four piston strokes. Namely, (1) an intake stroke during which a piston moves within a cylinder to draw in an air/fuel mixture, (2) a compression stroke during which the air/fuel mixture is compressed between the piston and a cylinder head, (3) a power stroke during which combustion of the air/fuel mixture drives the piston along the cylinder to create work, and (4) an exhaust stroke during which exhaust gases resulting from combustion are expelled from the cylinder. In contrast, in a two-stroke system, the four parts of the combustion process are condensed to two piston strokes, (1) an intake/compression stroke and (2) a power/exhaust stroke. Two-stroke petrol (gas) engines are generally employed with high-power, handheld applications such as lawn mowers, trimmers, outboard motors, motorcycles and chain saws. Diesel engines rely on heat produced during compression to ignite a fuel/air mixture. Two stroke diesel engines are used in many large industrial and marine applications
Loop scavenged two-stroke diesel engines employ transfer ports that are shaped and positioned to direct a fresh mixture of air/fuel toward the combustion chamber. The air/fuel mixture strikes the cylinder head, follows a curvature of the combustion chamber, and is then deflected downward. The downward deflection prevents the fuel/air mixture from traveling directly out of the exhaust port along with the exhaust gases and also creates a swirling turbulence that improves combustion efficiency, power and economy. In a turbo-charged loop scavenged two-stroke diesel engine, during the power/exhaust stroke, compressed air from a compressor portion of a turbocharger is guided into the combustion chamber through an inlet port. The compressed air helps drive exhaust gases through an exhaust port as well as mixing with fuel during the intake/compression stroke to contribute to the combustion process.
During a portion of the power/exhaust stroke, the exhaust gases loose pressure and thus contribute very little to driving the turbine portion of the turbocharger. Further, at the lower pressure, the exhaust gases often times may reduce turbine/engine operational efficiency. Accordingly, it is desirable to provide a system that redirects exhaust gases from the turbine portion of the turbo-charger during a portion of the power/exhaust stroke of the piston.